Electronic systems and circuits have made a significant contribution towards the advancement of modern society and are utilized in a number of applications to achieve advantageous results. Numerous electronic technologies such as digital computers, calculators, audio devices, video equipment, and telephone systems facilitate increased productivity and cost reduction in analyzing and communicating data, ideas and trends in most areas of business, science, education and entertainment. Many of the electronic systems that provide these advantageous results often utilize switch circuits to connect to a voltage source. However, traditional attempts at connecting to multiple voltage levels often involve a variety of issues.
FIG. 1 shows a block diagram of a conventional super-high-voltage (SHV) switch circuit. In the conventional switch circuit, signal Vpp_in is the input with the voltage ranging from OV to the value of the super-high-voltage (SHV). The switch driver has two PMOS devices. Device M1 is the driver that drives Vpp_out to Vpp_in and device M2 serves as a keeper. When Vpp_in is at or below vpwr (stage 1), vdrive is pulled low turning on keeper transistor M2. When Vpp out is at vpwr the conventional circuit operates in normal mode. When Vpp_in is raised to a threshold (Vtp) above vpwr (stage 2), the switch is still in normal mode. Transistor MO turns on causing vdrive to start rising. At the same time, transistor M1 turns on because the Vgs of transistor M1 has reached a threshold. The current can start leaking through transistor M1 and transistor M2. When Vpp_in reaches above Vtrip (stage 3), Vpp_out is switched over to Vpp_in and the circuit is now in SHV mode.
Conventional circuit architectures can encounter difficulties at lower voltage processes. The gate-source voltage (Vgs) of M1 is the difference between Vpp_in and vpwr and there is a potential concern of device breakdown on the driver MI. In one exemplary process that implements the conventional design, the maximum SHV is 8.75V and the minimum vpwr is 1.6V. The Vgs of M1 can be as much as 7.15V while the junction breakdown voltage is only 5.5V. Another difficulty encountered in conventional approaches includes leakage current issues. When Vpp_in reaches a P-type threshold voltage (Vtp) above vpwr, driver M1 in FIG. 1 begins to turn on. The conventional design relies on the keeper M2 to sink enough current to prevent the circuit from switching over to SHV mode.
Conventional approaches also can encounter difficulties in effectively preventing false switching. It can be very difficult for the conventional design to set the Vtrip to be a few P-type threshold voltages (Vtp's) above the vpwr. Furthermore, it is often problematic for keeper M2 to sink sufficient current to keep the output at vpwr when relatively large current is driven through the switch driver to the output. It is also often difficult for the output Vpp_out to be pulled low in normal mode because of the keeper M2.